The anatomy of a tooth is well known with an inner dentin layer and an outer hard surface enamel layer. Enamel is an opaque white or off-white color. It is the enamel that can become stained and/or discolored. The porous nature of the enamel layer allows stain and discoloring substances to enter the enamel surface and thereby discolor the tooth.
Many substances and food items, such as juices, tea, coffee and tobacco, can "stain" or reduce the "whiteness" of teeth. These substances are consumed on a daily basis and gradually over several months or years can impart a noticeable discoloration of the enamel surfaces of the teeth.
Presently the dental profession uses methods to whiten teeth that are based on the presentation of either hydrogen peroxide or carbamide peroxide in a gel preparation to the enamel surfaces of the teeth. These compounds come in varying strengths from 10 wt. % to 35 wt. %. The gels are delivered either by the dentist in the dental office, accompanied by light and/or heat, or by using home-use kits via plastic trays fitted to the teeth.
The home-use kits, which use low concentration compounds, require the fabrication of a plastic tray filled with a whitening gel before placement over the teeth. For proper fitting, a dentist must usually fabricate the tray. The treatment time is high and the activities of the consumer are restricted while the tray is in place. Generally several treatments are required. The disadvantage of this system is the lengthy time required to whiten teeth and the high inconvenience accompanying its use.
Faster whitening is accomplished by the dentist in the office, where the higher concentration gels are used. However, the cost to the consumer is higher and there is additional risk of the higher concentrations causing some soft tissue irritation. There is a demand in the marketplace for a less costly and more easily utilized whitening product which is without the constraints on time, the mess of the gels and lack of dental trays.
Candies, tablets, gums, and the like have been used as a vehicle for introducing various chemical agents to a tooth surface. A strict requirement, however, for these compositions is that they have a long shelf-life, at least on the order of several weeks. This requirement has limited the use of solids for tooth-whitening preparations, because in general the active components for tooth-whitening are not stable under ambient conditions of humidity and temperature. In solid compositions, these active components quickly become degraded to unsuitably low concentrations. In addition, the whitening compositions frequently degrade to reactions products with a bad taste. Thus, the compositions can become unpalatable even before the active component has degraded to insufficient levels.
An example of a tablet or gum or tooth treatment is disclosed in U.S. Pat. No. 4,302,441 issued to Muhlemann et al. on Nov. 24, 1981. This patent discloses a solid oral preparation comprising active urea hydrogen peroxide (carbamide peroxide) that is effective in countering acid fermentable carbohydrates in dental plaques. The solid oral composition in the form of a lozenge tablet or chewing gum comprises urea hydrogen peroxide and, in the absence of glycerol, and a sweetener selected from the group consisting of mannitol, sorbitol, xylitol and saccharin, and a carrier selected from the group consisting of soluble cellulose ethers and carbohydrate gums. These compositions may be effective in introducing carbamide peroxide to the surface of the teeth of the person to whom it is administered, but they suffer from having a short shelf life. In solid materials carbamide peroxide gradually reacts with ambient water such as from humidity in the air and with water in the composition to form urea and oxygen or hydrogen peroxide. This not only leads to a decrease in the effective amount of the carbamide peroxide, it also produces urea, which in small concentrations lends a sharp, unpleasant taste to the composition. Thus, even before the composition becomes ineffective from depletion of the carbamide peroxide it becomes unpalatable in only a few days and unacceptable as a consumer product.
Objects of the Invention
It is, therefore, an object of the invention to provide a system for delivering whitening agents to tooth surfaces that overcomes the shortcomings of the prior-art gel systems.
It is also an object of the invention to provide a whitening composition with a long shelf-life that does not degrade quickly to become unpalatable or ineffective.
An object of the invention is also to provide a system that is less costly and can be used by the consumer in a manner that does not restrict activity and requires an undue amount of time.
It is further an object of the invention to provide a composition in a solid form that is commercially acceptable, that is, introduces a sufficient carbamide peroxide to the tooth surface to provide a whitening effect, but also to provide sufficient stability that the product over a storage period of several weeks will not decompose to form urea to give the product an unpleasant taste.
It is further an object of the invention to provide a system that avoids the messy gels and liquids, and high peroxide concentrations.
Further objects of the invention will become evident in the description below.